My first 29 -- 114mm cranks?

Alright, I’m about to add a 3rd unicycle to my collection, and would like some shopping advice.

My current plan is to buy a Nimbus 29" Touring Unicycle with 114mm cranks from UDC. I have never ridden a 29er before and most of my riding will be in town/commuting.

I’m choosing 114mm cranks for a little extra speed and because I don’t think I’ll do much riding that will require the extra torque (I can make it up all the hills in town just fine with 152s on my 24 Torker). Would anyone recommend that I just go straight down to 100mm (given that I don’t mind dealing with a slower learning curve)? If I did that, how difficult would that make hills become? Could it be uncomfortable at all? Should I consider 125s?

I think 114’s are a good choice. I use them on my 36er, so it should be fine for yiour 29er too. They are not the shortest cranks, but a good overall medium length for both 36er and 29er.

I suggest 125s may be a safer compromise.

You’re going for a bigger wheel than you’re used to and a shorter crank at the same time.

I alternate between 114s and 125s on my 28 according to my mood and the weather. It’s not just the torque on the hills, but every time you speed up, slow down, stop, reverse or idle that you will notice the difference.

I have something like a 28" and it has 102s on it. I really like them for the speed, but they make emergency stops hard.

Cranks doesnt cost that much, i started with 125mm and went down to 114. 125 to get used with the wheel first time and then 114 for the sped :wink:

Crank length

On my 29" I use 125 and 104, mostly 125.
I find the 125’s a good compromise for commuting, hills, off roading.

I always found 150 too hard on my knee’s but best bet is to go with what you feel comfortable.

The 104’s make idling harder, sudden stops harder, and down hill harder, but they can increase top speed marginally.

Also, the shorter stroke of shorter cranks uses a smaller part of the muscle movement that is available, so it can become more tiring.

On the whole, there is a limit to how much torque you can apply, but you can always learn to spin faster for longer. On this basis, slightly longer cranks are more versatile.

I rode my 28 on 80mm cranks once. It ended up in the canal.

If you put it in relative terms the torque on the 29 with 114’s would be something like what you might have on your 24 with 80’s.

I think for starters 125’s are good on the 29’er, and you might want to pick up the 114’s at the same time, because you will be switching at some point.

I found that the 125’s were the most comfortable across the range of what I liked to ride including commuting 4 miles, and XC.

Thanks for all the advice!

I’ve decided to buy both the 125s and 114s. I suppose I probably should have mentioned that I’m already used to 127s, although I’d still rather have shorter on a 20 (and I really wish I hadn’t started with 152s on my 24!).

They’ll be good, and if they’re challenging at first, ride more and they’ll get better. You can climb some decent inclines with cranks that short and good technique.

If I had to pick a single length to get stuck on my 29 for life, I’d probably choose 125, only because I use my 36 for distance, and my 29 for travel, XC, and intervals climbing. Fortunately, I don’t have to choose a length for life. I invested in a set of the tri-tapped Da Vinci’s, at 130/150/170. Haven’t used the 170 setting yet, and doubt I will. For flat, the 130 is workable, although I spend most of my riding miles on steep hills with the 150 setting.

Unicyclists seem to fall, the world over, for the simple conclusion that reducing the crank gives more speed. It crops up time and time again.

It is quite hard to apply a regular circular motion as you go for smaller and smaller circles. There comes a point where it becomes the opposite You don’t neccesarily increase your cadence by reducing the length of the circumference, there is a point where motor control is compromised sufficient to work against you.

As an illustration, there is a reason why bicyclists, after riding for a while and increasing their strength, go for the more time consuming and expensive option of changing cogs to up their speed. As opposed to simply swapping the cranks for shorter ones.

And while I maintain that there is a point where going shorter does not give you a faster rotational speed, it WILL continue to give you the DISBENEFIT of needing a lot more strength to simply maintain your ride - accelerating and decelerating as the bumps and troughs pass under your wheel for example.

In my case I actually opt for a little extra length - and as a result I am able to manage City of Perth bumpy paving, negotioate shopping pedestrian traffic on busy footpaths and all - all ona daily basis.

Please don’t get me wrong - you may get a speed increase from a shorter crank. Or you could in fact go slower. Just don’t fall for the superficial mechanical advantage argument for it. As no-one ever asks the question"will I get there faster if I INCREASE my crank from 100mm to…", it seems that people are indeed only coming from this high school physics simplification.

This debated so often in this forum. I’ve written a few thousand words on it myself.

What do we mean by speed?:

  • Peak top speed on the flat?
  • Comfortable cruising speed?
  • Average speed over a journey?
  • Speed of acceleration/deceleration (responsiveness)

There are other variables such as the weight of the wheel/tyre (heavier = smoother = faster cruising); the section and pressure of the tyre; the skill and style of the rider…

Peak top speed over a short distance will be increased by shorter cranks - that’s why there is a minimum crank length for track racing.

In most other categories, there comes a point when shorter cranks become counterproductive.

I write as someone who has experimented with most sizes between 80mm and 170mm over several years. I’ve now chosen 150mm for Muni, 125 for general riding, and 114 for fast and flat.

I am also considering a new crank arm on a 29er for a 3 day 100 mile charity ride. It is a flat ride on a pulverized stone surface - about as close to paved as you can get without actually being paved. I don’t have any experience with shorter cranks that 125mm but I recalled that Lars Clausen used 125mm on his Coker for moderate terrain and 150mm cranks for hilly terrian. So it seemed to me that 100mm cranks would be a good choice for the 29er on flat terrain since that is the same total gear ratio as the coker with 125mm cranks. However, given Mike’s experience there must be more to the equation than simply the total gear ratio. What am I missing? I do understand that the 100mm cranks on the 29er will mean more revolutions for the same distance than the 125mm cranks on the coker but otherwise I would have thought that they would have been equally easy (or difficult) to control. I’m starting to rethink my choice - maybe the 114 cranks would be the safest bet.

Also keep in mind that with a coker, you have much more rotational mass that actually helps keep the wheel turning; it’s almost like a “flywheel” effect, especially on flat. The 29er is MUCH lighter, with a lot less rotational mass, so I’m not sure the comparison is totally valid.

This really is a case where you may benefit from using the search function.

There is an “Official” 29 discussion thread. You will aso find references (using “Advanced Search”) to the “CFSH” and “Constant Foot Speed Hypothesis”.

General rules:

Shorter cranks tend to be faster only up to the point where the rider is 100% confident of control.

Assuming you can idle at all, then if your cranks are too short for you to idle, they are too short for general use.

Simple thought experiments:

If short cranks automatically mean more speed, why is no one riding 10mm cranks?

If long cranks automatically mean more torque, why is no one using 250mm cranks?

Actually, I had searched the threads some time ago and found someone (Nathan, I think) that was very happy with the 100mm cranks with on the 29er but as you say the skill of the rider has a lot do to with it. I have tried a friend’s coker with the 125mm cranks and reasoned that if I could handle that then the 29er with the 100mm cranks would handle much the same. As Terry points out, however, this may not be a valid comparison. I’m going to go with the 114 cranks instead for flat and fast.



The verdict!

Alright, so in the end, I bought the unicycle with 115mm cranks, and switched to 145mm two weeks later. I love the 115s! I just feel like I’m floating right along on them. They’re really fast, smooth and comfortable and I can turn and maneuver just fine on them. They’re definitely great if you’re just commuting. However, when I tried the 145s, there was a huge difference, and it turns out that I like them too!

The 145s:
My first impression was, “These are huge and completely pointless, all this leg movement is uncomfortable” and while it’s true that they sorta suck if your just riding along, they really shine when it comes to more technical riding. Immediately, I was able to freemount (rollback mount instead of jump mount) without ant effort, idle indefinitely and ride backwards or with the seat out. It’s really easy to control speed and ride over obstacles, and feels a lot more like my smaller unicycles.

So in the end, I like both sizes and am glad I didn’t just stick to one.

Now this brings up another question: Does the same radius-to-crank ratio really feel the same on all unicycles? 145s on a 29, should correspond to
100s on a 20, but is the comparison between such different wheel sizes completely valid? If so, 180s on a 36 would be the next step and that certainly doesn’t seem quite right to me. Besides that, shouldn’t wheel weight make a huge difference as well?

I dont own a 29" but I ride 114mm on my Coker. The first time ever I tried a Coker it had 125mm cranks. Then I tried another one the same day with 114mm. I loved the 114mm and that’s what I started with on my Coker:) I love them!

I also tried 89mm. I loved them for the few revs I did until they stripped. I might try them again next summer, they’re doing pretty well on my 12" so they should be good for a little ride on the 36:)

Hi, I have Nimbus 29" and I’m using KH Twins 125/150. For paved roads or pretty flat and hard offroad I’m using 125 as riding 150 on a hard surface makes me feel bouncy… but on the other hand some XC seems impossible to me without 150 and now we have loads of snow in Poland and it feels far more comfy to use 150s in the snow.
But yeah… for the road use 125s seem to be the upper limit and a very comfortable one in my opinion.

I used 125s on my 29" when it was new. Except for free mounting, I liked them on easy, mostly flat rides. Yesterday I tried the 125s on my 36" for the first time. I found that 125s on the 36" are a lot easier than on the 29" (except for free mounting). I’m far happier with the 125s than the 150s on the 36". My question is, what are the cheapest 114s I can buy for KH frames? I don’t want to invest much since I may not like them.